Family resemblance for fasting blood glucose in a population of Japanese Americans

The Cincinnati lipid research clinic family study: Analysis of commingling and family resemblance for fasting blood glucose

Our specific aim in this study was to investigate commingling and family resemblance for fasting blood glucose in 160 randomly selected white families from the Princeton School District Lipid Research Clinics Family Study. Adjustment of fasting blood glucose for the influence of age, sex, and the use of oral contraceptives and construction of indices were performed simultaneously using multiple regression methods. Path analysis was carried out, constructing an environmental index based on special diet usage, hematocrit, and obesity, which was also adjusted for the influences of age and sex. Commingling analysis and segregation analysis using the mixed model were also performed. Nearly 16% of the variance of fasting blood glucose was accounted for by age and sex. Obesity itself, which constituted the index, explained an additional 4% of the variance of fasting blood glucose. Significant genetic heritability for fasting blood glucose was documented by both path analysis and segregation analysis. In aggregate, we conclude that though there was a major familial vector accounting for within-family aggregation of blood glucose, it was probably generated by a multifactorial component as compared to a major locus. Under the most parsimonious model, path analysis estimated the genetic and cultural heritabilities as h2 = .39 +/- .08 and c2 = .06 +/- .03., respectively.

Family studies of non-insulin-dependent diabetes mellitus in South Indians

Though a genetic basis for non-insulin-dependent diabetes mellitus (NIDDM) is clear, the likely mode of inheritance is not known. The segregation of NIDDM was studied in 64 nuclear South Indian pedigrees (449 individuals) ascertained through an affected proband having both parents and more than 1 sibling alive and available for oral glucose tolerance testing. A high proportion of parents were found to be of abnormal glucose tolerance [89 of 128 (70%) diabetic and 11 of 128 (9%) impaired]. Complex segregation analysis was performed using (1) POINTER which implements the mixed model and distinguishes major gene, multifactorial and non-transmitted environmental contributions to affection and (2) COMDS which implements an oligogenic model with major gene, modifier gene and environmental contributions to a) affection and b) diathesis (an ordered polychotomy amongst non-affected family members, based on 2-h plasma glucose level). Using POINTER, there was no formal support for a major gene and the most parsimonious solutions were achieved with multifactorial models. Using COMDS, we found i) significant improvements in models when information on glucose levels in nondiabetic family members (diathesis) was included, ii) support for segregation of a diallelic gene as well as background familial resemblance, and iii) under the best-supported model, this diallelic locus featured incomplete dominance (d = 0.8) and a disease-predisposing allele frequency of 14%. In South Indians, segregation of NIDDM is inadequately described by simple major gene models: more complex models provide more satisfactory descriptions. This finding, if applicable in other populations, has important implications for the search for diabetes-susceptibility genes.

Commingling and complex segregation analysis of fasting plasma glucose in the Lipid Research Clinics family study

Commingling and segregation patterns of fasting plasma glucose (GL) were examined in family data from 5 clinics (Cincinnati, Stanford, Iowa, Minnesota, and Oklahoma) of the Lipid Research Clinics (LRC) family study. In addition to the primary question of whether there was a major gene for GL, a secondary purpose was to investigate the possibility of genetic heterogeneity among the 5 clinics. No statistical support was found for heterogeneity among clinics, either in the commingling of distributions or in the segregation patterns. For the combined clinics sample, both a major effect and a multifactorial component were significant. However, the major effect (accounting for 73% of the variance) was not found to be consistent with a major gene, as the hypothesis of Mendelian transmission was rejected. The most parsimonious model involved equal transmission probabilities, which suggests that the major effect is not transmitted from parents to offspring. Possible sources of this major non-Mendelian effect were explored. The multifactorial component accounted for 10% of the variance in GL levels, and no generational differences were noted. Although our study was unable to provide evidence in favor of a major gene effect, it should be noted that a major gene cannot be firmly refuted. For example, a variety of interactions, such as genotype-dependent age effects, could have masked the transmission probabilities.

Family resemblance for fasting blood glucose: the Jerusalem Lipid Research Clinic

Familial aggregation of fasting plasma glucose was studied in a sample of families examined at the Jerusalem Lipid Research Clinic. We first examined homogeneity of familial correlations across major origin groups in the Israeli sample. Correlations were generally homogeneous across origin groups, except for mother-son pairs. The pooled familial correlations were relatively low for unadjusted blood glucose values, and somewhat higher upon adjustment for sex, age, ethnicity, education, seasonality, body mass, cigarette smoking, alcohol consumption and dietary intake. Genetic and cultural determinants of blood glucose were estimated utilizing a path model with 10 parameters to be estimated from a total of 16 correlations. Under a reduced model genetic heritability (h2) was estimated to be 0.18 +/- 0.08 and cultural heritability (c2) was 0.10 +/- 0.02. However, within this population the additive variation could be explained by a cultural model of inheritance without introducing genetic parameters, and most of the variance is due to "random" unmeasured environmental factors. Commingling analysis was also performed, and our findings imply that there is no evidence for admixture in the distribution of fasting blood glucose in this Israeli population sample.